Developments in the art of electrophotographic copiers have tended to increase both the copying rate and the versatility of the system, while simplifying operative and corrective problems for an operator. Thus high speed copiers are in use which are capable of providing in excess of 75 copies per minute. Along with this it is desirable to provide such features as duplex (two sided) copies of simplex (one sided) masters and duplex copies of duplex masters, all in selectable multiples. The jam condition is detected and indicated automatically, and the number of copy documents made may also be indicated automatically. When a jam occurs, this must be cleared by the operator, but it is desirable that the operator not be required to take the time or make the judgements needed to find and position the proper master, set the machine accordingly, and reinitiate the procedure.
A substantial time disparity can exist in such a system between the completion of image transfer from the master to the imaging system (e.g. an electrostatic drum) and the final delivery of the last reproduced copy to an output device (e.g. an exit tray). As the art has progressed, the amount of exposure time needed has been reduced to a fraction of a second and transport speeds have increased so that total cycle times are now measured in milliseconds rather than seconds. During the interval in which the last reproduced copy is moving out of the system there can be a substantial delay while the copy passes along a long transfer path in which a jam might occur. If a jam occurs somewhere in the copy transport mechanism, the operator must not only clear the jam but restart the copy sequence by resinserting the master. This is particularly troublesome with duplex operations, because the longer and more complex flow path to be followed by the copy documents creates greater susceptibility to jams, and the handling procedure for both originals and copies becomes substantially more complex. If a jam does not occur, the system must further delay operations until the next succeeding master is moved into position. These factors can substantially reduce the throughput of the machine.
In attempting to confront these and other practical problems, semiautomatic and automatic document handlers have been provided in the prior art, of which U.S. Pat. Nos. 3,747,918 and 3,790,158 are examples. It is further known, as evidenced by U.S. Pat. No. 3,588,472, to incorporate control logic and sensors into a system, to track copying in the event that a jam occurs, and to count the number of copies successfully provided. It is also known to recirculate masters to an entry tray after copies have been made, as shown by U.S. Pat. No. 3,790,158. In this system, a master that has been copied is returned to the document supply tray and is stacked on top of a movable ball which separates the copied masters from those yet to be copied.
A particularly versatile example of a semi-automatic document feed system is shown in U.S. Pat. No. 4,090,787 entitled "Automatic Copier Mode Controls" and issued to James Henry Hubbard et al. The referenced patent describes operation in both simplex and duplex modes, as well as the performance of a substantial number of control functions. The prior art has not, as far as is known, provided reliable and inexpensive systems which allow reinitiation of copying procedures in a variety of simplex and duplex modes, while automatically recalling the needed one or two masters for completion of the run, after clearance of a jam.